The present disclosure relates to machinery with rotating shafts and more particularly, to centering springs and dampers used with bearings and shafts in an engine.
Rotating shafts and other rotating turbomachinery in engines are supported by arrays of antifriction bearings connected to nonrotating structures. During operation, the rotating shafts and other rotating turbomachinery can vibrate about the engine centerline. If not dampened, these vibrations can cause excessive structural loads and result in damage. Dampers are used adjacent to the bearings to reduce the amplitudes of vibrations in the rotating shaft that are transmitted to the rest of the engine. Coulomb and viscous dampers are two of a variety of dampers that can be utilized. One commonly used viscous damper is the squeeze film damper, which utilizes a small, fluid-filled annular gap between the bearing and a nonrotating housing. Radial motion of the rotating shaft causes relative motion between the bearing and the nonrotating housing, which changes the gap to squeeze a damping fluid within the annulus, dampening the motion of the rotating shaft. The nonrotating housing and the bearing are usually connected by a centering spring to support the rotating shaft and to move the bearing and shaft towards the centerline when they become off centered. A centering spring design known as the squirrel cage is often used to connect the housing to the bearing and is comprised of a plurality of circumferentially spaced beam springs, acting as the centering springs. Squirrel cages have several notable disadvantages. First, they tend to be axially long and may require increased engine length, adversely impacting weight and major performance metrics. Second, the beam springs of the squirrel cage must be machined into the damper assembly and/or the bearing, which causes additional manufacturing and installation time, and the entire assembly must be replaced if one of those beam springs or the damping surface is damaged. Third, the squirrel cage imposes undesirable resultant moments on its mating housing.